Synthesis of Iron-Doped Manganese Oxides with ... - ACS Publications

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Synthesis of Iron-Doped Manganese Oxides with an Ion-Sieve Property: Lithium Adsorption from Bolivian Brine Ramesh Chitrakar,† Yoji Makita,† Kenta Ooi,‡ and Akinari Sonoda*,† †

Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2217-14 Hayashi-cho, Takamatsu, Kagawa 761-0395, Japan ‡ The Institute for Environmental Management Technology, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan ABSTRACT: Iron-doped lithium manganese oxides Li1.33FexMn1.67−xO4 (x = 0.15, 0.30, and 0.40) were prepared by calcination of carbonates of Li, Mn, and nitrate of Fe in air at 350, 400, 450, 550, and 650 °C. The calcined samples, characterized by X-ray diffraction (XRD) and chemical analysis, were spinels. The protonated samples after treatment with HCl solution were tested as adsorbents for lithium adsorption from the salt lake brine collected from the Salar de Uyuni, Bolivia. The precursor showed 3.7% Mn extraction upon acid treatment with Fe/Mn ratio of 0.1 obtained from calcination at 450 °C. The amount of Mn extracted in HCl solution decreased with increasing of Fe/Mn ratio, and the amounts of lithium extraction were 90%, 96%, and 91% for Fe/ Mn = 0.1, Fe/Mn = 0.2, and Fe/Mn = 0.3, respectively, while the amounts of dissolved iron showed the opposite trend. By studying the lithium adsorption in the raw brine and NaOH-added brine by a batch method, the adsorbent with Fe/Mn ratio of 0.1 obtained from calcination of the precursor at 450 °C was found to be efficient lithium adsorbent with lithium uptake of 18 mg/g at final pH 2.0 from the raw brine (initial pH 6.7) and 28 mg/g at final pH 7.2 from the NaOH-added brine (initial pH 8.2). The adsorbent with Fe/Mn ratio of 0.1 obtained from calcination of the precursor at 450 °C was evaluated for a 4 cycle adsorption/desorption experiment. The amount of manganese extracted (%) in the solution decreased with cycle numbers, 1.1% in the first cycle and 0.70% in the fourth cycle.

1. INTRODUCTION Increasing attention is being paid to lithium due to the growing market for lithium based rechargeable batteries in mobile information, communication technologies, and electric vehicles.1 Lithium is mostly obtained from two main resources: spodumene and petalite ores and salt lake brines.2 Salt lake brines containing high concentrations of lithium are found in Chile, Argentina, Bolivia, USA, and China.3,4 A variety of technologies and materials have been evaluated as a means for recovery of lithium from the brines. Commercial operations for recovery of lithium from salt lake brines in Chile, Argentina, USA, and China are based on the solar evaporation process in several stages to concentrate the brine, requiring several months until it shows a higher lithium grade (∼6% Li).2,5 Although the Salar de Uyuni in Bolivia has the largest known deposits of lithium in the world, lithium production processes are currently under development stage because of the unfavorable conditions of high concentrations of magnesium in the brines.5 The common method such as the coprecipitation method consists of the addition of aluminum chloride to the brine by adjusting the pH with NaOH solution to obtain lithium aluminum hydroxide, but the method is complex depending on many variables such as Al/Li molar ratio, pH, temperature, and stirring time.6,7 Recently, a new electrochemical method was reported for recovery of lithium from brine:8 a battery composed of a lithium capturing cationic electrode (LiFePO4) and a chloride capturing anodic electrode (Ag) was immersed in 5 mol/dm3 NaCl solution used as brine with Li/Na molar ratios of 1/1000 and 1/10 000. This battery can convert a © 2014 American Chemical Society

sodium-rich solution (Li/Na = 1:100) into a lithium-rich solution (Li/Na = 5:1) by consuming 144 W h/kg of lithium recovered. A hydrometallurgical method based on two-stage precipitation was developed for lithium recovery from the brine of Salar de Uyuni, Bolivia.9 This method consists of several steps such as addition of lime to the brine for precipitation of Mg and Ca followed by a solar evaporation process to recover lithium. In the past, ion-sieve manganese oxides of various compositions were explored to study lithium adsorption from the solutions.10−15 Very recently, we adopted the ion-exchange method using ion-sieve manganese oxides H1.33Mn1.67O4 and H1.6Mn1.6O4 for recovery of lithium from the brine in a laboratory scale: lithium was adsorbed into the manganese oxides, and recovery of lithium was done by elution with HCl solution.16 The ion-exchange property of Fe-doped lithium manganese oxides with spinel structures is relatively little explored compared to the electrochemical properties.17−22 Liu et al.17 studied lithium extraction/insertion reaction in aqueous solutions of LiCl and LiOH with LiFeMnO4 spinels (Fe/Mn = 1) prepared by a coprecipitation method. The manganese mineral usually contains iron,23 so the iron-doped adsorbent prepared directly from the manganese mineral can be an inexpensive adsorbent. Received: Revised: Accepted: Published: 3682

December 24, 2013 February 6, 2014 February 14, 2014 February 14, 2014 dx.doi.org/10.1021/ie4043642 | Ind. Eng. Chem. Res. 2014, 53, 3682−3688

Industrial & Engineering Chemistry Research

Article

Table 1. Composition and Lattice Parameter of the Calcined Samples T (°C)

sample

chemical composition

oxygen/cation

ZMn

a (nm)

350 400 450 450 450 550 650

FeMn-0.1-350 FeMn-0.1-400 FeMn-0.1-450 FeMn-0.2-450 FeMn-0.3-450 FeMn-0.1-550 FeMn-0.1-650

Li1.35Fe0.17Mn(III)0.37Mn(IV)1.26O4 Li1.32Fe0.17Mn(III)0.21Mn(IV)1.39O4 Li1.32Fe0.17Mn(III)0.21Mn(IV)1.39O4 Li1.20Fe0.31Mn(III)0.17Mn(IV)1.34O4 Li1.13Fe0.44Mn(III)0.17Mn(IV)1.26O4 Li1.36Fe0.18Mn(III)0.31Mn(IV)1.29O4 Li1.37Fe0.18Mn(III)0.34Mn(IV)1.27O4

1.27 1.29 1.29 1.32 1.33 1.27 1.27

3.77 3.87 3.87 3.89 3.88 3.81 3.79

0.819 0.813 0.816 0.813 0.812 0.816 0.817

Table 2. Composition and Lattice Parameter of the Protonated Samples sample

chemical composition

oxygen/cation

ZMn

a (nm)

FeMn-0.1-350(H) FeMn-0.1-400(H) FeMn-0.1-450(H) FeMn-0.2-450(H) FeMn-0.3-450(H) FeMn-0.1-550(H) FeMn-0.1-650(H)

Li0.07H1.11Fe0.05Mn(III)0.03Mn(IV)1.64O4 Li0.05H1.24Fe0.11Mn(III)0.06Mn(IV)1.55O4 Li0.10H1.17Fe0.15Mn(III)0.05Mn(IV)1.53O4 Li0.10H1.21Fe0.27Mn(III)0.10Mn(IV)1.40O4 Li0.13H1.00Fe0.40Mn(III)0.09Mn(IV)1.35O4 Li0.19H0.97Fe0.15Mn(III)0.07Mn(IV)1.55O4 Li0.51H0.70Fe0.16Mn(III)0.05Mn(IV)1.54O4

1.38 1.33 1.33 1.30 1.35 1.36 1.35

3.98 3.96 3.97 3.93 3.94 3.96 3.97

0.808 0.808 0.808 0.807 0.806 0.806 0.807

2100; Rigaku Corp.) operated at 40 kV voltage and 24 mA current with Cu Kα radiation. The XRD patterns were recorded in the range of 5−70° (2θ) at a scanning rate of 1° (2θ)/min. The cubic lattice constant (a) was determined using a JADE 3.0 package. Thermogravimetric-differential thermo analysis data (TG-DTA) of the sample were recorded using thermal analyzer (Rigaku Thermo plus TG 8110) at a heating rate of 10 °C/min in air. Chemical Analysis. Samples (0.05 g) were dissolved in 5 cm3 of HCl solution (5 mol/dm3) containing a few drops of 30% H2O2 followed by heating around 80 °C to dissolve Fe and Mn, and the final volume was adjusted to 100 cm3 with deionized water. The resulting solutions were analyzed for their Li, Mn, and Fe contents after appropriate dilutions by atomic absorption spectrometry (AAnalyst 300; Perkin-Elmer). The mean oxidation state of Mn (ZMn) was evaluated after determination of active oxygen by the standard oxalic acid method.10 Salt Lake Brine. Raw brine of Salar de Uyuni, Bolivia was supplied by Japan Oil, Gas and Metals National Corporation (JOGMEC). The raw brine was analyzed for its Li, Na, K, Mg, and Ca contents (three replicate analyses) by atomic absorption spectrometry and Cl, NO3, and SO4 (three replicate analyses) by ion chromatography (761 Compact IC: Metrohm AG). The concentrations of ions (mg/dm3) in the raw brine are as follows: Li = 1630, Na = 59 000, K = 18 700, Mg = 29 000, Ca = 230, Cl = 240 000, SO4 = 26 000, and NO3 = 970. Since NaHCO3 acts as a buffer in the brine, NaHCO3 (25 g) was added to the raw brine (1.0 dm3) to control pH around 6.3−6.5 in lithium adsorption experiments. In other separate experiments, 1 mol/dm3 NaOH was added to the raw brine to study the lithium adsorption at different final pHs (pH 2.0−7.2). Lithium Adsorption/Desorption in the NaHCO 3Added Brine. In lithium adsorption experiments, the adsorbents (1.0 g) were immersed in the NaHCO3-added brine (50.0 cm3) and kept under magnetic stirring at room temperature for 1 d. The suspensions were filtered, washed with deionized water, and finally dried at room temperature. The resulting solutions were analyzed for their lithium contents. For lithium desorption experiments, lithium-loaded adsorbent (1.0 g) was treated with 0.5 mol/dm3 HCl (80 cm3) and kept under

The effect of iron doping in manganese oxides on lithium adsorption properties from the salt lake brine has not been explored yet. In this study, we report the synthesis of irondoped lithium manganese oxides by solid-state reaction and we discuss the effect of iron doping on the adsorption of lithium ions from the salt lake brine.

2. EXPERIMENTAL SECTION Synthesis of Iron-Doped Lithium Manganese Oxides. Li1.33FexMn1.67−xO4 (x = 0.15, 0.30, and 0.40) samples were synthesized by solid-state reaction. Reagent-grade chemicals of Li2CO3 (99%), MnCO3 (95%), and Fe(NO3)3·9H2O (98%) (Wako Pure Chemicals Industries, Ltd. Japan) were used as starting materials. First, Li2CO3 was ground for 10 min in an agate mortar. Also, separately Fe(NO3)3·9H2O was ground for 10 min. Stoichiometric amounts of the starting materials (Li, Mn, Fe) were mixed and further ground for 10 min and calcined for 4 h in air at 350, 400, 450, 550, or 650 °C followed by cooling to room temperature. The samples were designated as FeMn-R-T, where R is 0.1, 0.2, or 0.3 corresponding to Fe/ Mn ratio and T is 350, 400, 450, 550, or 650 corresponding to calcination temperature (Table 1). Lithium Extraction from the Precursors. Iron-doped manganese oxide adsorbents were prepared by adding the precursor (2.5 g) into 200 cm3 HCl solution (0.5 mol/dm3) in a beaker, and the mixture was kept under magnetic stirring for 1 d at room temperature. The adsorbents were filtered, washed with deionized water, and finally dried at room temperature. The resulting solutions were analyzed for their Li, Mn, and Fe contents. The adsorbents were designated as FeMn-R-T(H), where R is 0.1, 0.2, or 0.3 corresponding to starting Fe/Mn ratio, T is 350, 400, 450, 550, or 650 corresponding to the calcination temperature of the precursor, and H is the protonated product (Table 2). The amount of Li, Mn, or Fe extracted (%) was calculated as follows: [amount of Li, Mn, or Fe extracted (mg/g)]sol. /[total Li, Mn, or Fe content (mg/g)]ads. × 100

Physical Analysis. Powder X-ray diffraction analysis (XRD) was carried out by an X-ray diffractometer (RINT 3683

dx.doi.org/10.1021/ie4043642 | Ind. Eng. Chem. Res. 2014, 53, 3682−3688


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magnetic stirring for 1 d at room temperature. The filtrates were analyzed for their Li, Mn, and Fe contents. Lithium Adsorption in the NaOH-Added Brine. NaOHadded brine solutions were prepared by adding a known volume of 1 mol/dm3 NaOH into the brine at various volume ratios of 0, 0.02, 0.04, 0.06, 0.08, 0.10, and 0.12. The adsorbent (0.20 g) was weighed into a test tube containing 10.0 cm3 of NaOH/brine at various volume ratios, and the mixture was occasionally shaken at room temperature for 1 d. The suspensions were filtered, and the resulting solutions were analyzed for their pH and lithium contents. Effect of Adsorbent Dose on Lithium Adsorption in the NaOH-Added Brine. The effect of adsorbent dose on lithium adsorption in the NaOH-added brine (NaOH/brine = 0.10, volume ratio) was carried out; a total of 0.20−1.0 g of adsorbent was weighed into a test tube containing 20.0 cm3 of the brine, and the mixture was occasionally shaken for 1 d at room temperature. The suspensions were filtered, and the resulting solutions were analyzed for their lithium contents. Kinetic Studies. Rate of lithium adsorption from the NaOH-added brine (NaOH/brine = 0.10, volume ratio) was carried out at various reaction times (0.5, 1, 2, 4, 6, 8, and 24 h). For each experiment, the adsorbent (0.20 g) was weighed into a test tube containing 10.0 cm3 of the brine, and the mixture was occasionally shaken at room temperature for the designated times. The suspensions from various reaction times were filtered, and the resulting solutions were analyzed for their lithium contents. Regeneration. Adsorbent of 2.0 g of lithium-loaded was treated for 4 h with 50 cm3 of HCl solution (0.5 mol/dm3). After this treatment, the adsorbent was separated by filtration, followed by washing with deionized water, and finally dried in air. The protonated adsorbent was dispersed in 100 cm3 of the NaOH-added brine (NaOH/brine = 0.10, volume ratio; initial pH 8.2). Adsorption/desorption experiments were performed up to 4 cycles.

Figure 1. (a) XRD patterns of iron-doped lithium manganese oxides; (b) their protonated samples (adsorbents). (×) Fe2O3.

discrepancy may be linked to a difference in the Mn3+/Mn4+ ratio and to variation in the concentration of oxygen vacancies.24,25 The general formula of spinel structure can be written as AB2O4, where A and B are cations occupying tetrahedral (8a) and octahedral (16d) sites, respectively, in a cubic closed packed array of oxygen atoms (32e) sites.26 The intensity of (111) peak in the XRD pattern is directly related to the amount of lithium occupying the tetrahedral (8a) sites of the spinel lattice.24 The appearance of (220) peak at 2θ (around 30°), which can be observed in the XRD patterns of the LiFeMnO4 spinel, suggested that iron ions partly occupied the tetrahedral (8a) sites of the spinel structure.17,18,24 The absence of the (220) peak in the present XRD patterns of the samples indicated that manganese and iron ions could occupy the octahedral (16d) sites.21 Table 1 shows the composition of the samples obtained by using a combination of chemical analysis data together with the mean oxidation state of manganese (ZMn) under the condition of electroneutrality.10 Most of the samples have an oxygen/ cation ratio close to 1.33, a value for a stoichiometric spinel.27 The oxygen/cation ratio in the spinels may be lesser or larger than 1.33, because it is very difficult to prepare or control irondoped lithium manganese oxide spinel with both exact oxygen stoichiometry and no cation vacancies.27 Lithium Extraction from the Precursors. The adsorbents can be prepared by the Li+/H+ exchange of the precursors with HCl solution. Figure 2 shows the amounts of lithium extraction and dissolved manganese and iron from the precursors with various Fe/Mn ratios (FeMn-0.1-450, FeMn-0.2-450, FeMn0.3-450) during treatment with HCl solution. The precursor showed 3.7% Mn extraction upon acid treatment with Fe/Mn

3. RESULTS AND DISCUSSION Synthesis of Iron-Doped Lithium Manganese Oxide Precursors. Figure 1a shows the powder X-ray diffraction patterns of iron-doped lithium manganese oxides with various Fe/Mn ratios prepared by calcination of LiCO3, MnCO3, and Fe(NO3)3 at 350−650 °C for 4 h in air. All the samples crystallized in the spinel structure as the main phase. Three samples (FeMn-0.1-350, FeMn-0.1-400, FeMn-0.1-450) exhibited the hkl peaks (111), (311), (222), (400), (331), (511), (440), and (531), which could be indexed to cubic spinel structure of Li1.33Mn1.67O4 with Fd3m space group (XRD patterns matched with Li1.33Mn1.67O4, JCPDS Card No. 460810). The intensity of (111) peaks in XRD patterns of other two samples (FeMn-0.1-550, FeMn-0.1-650) increased slightly with appearance of additional peaks (weak peaks indicated in Figure 1a by ×) that could not be indexed in a cubic spinel phase suggesting a small amount of impurity. This impurity arising from α-Fe2O3 had also been detected in iron-doped lithium manganese oxides prepared by the coprecipitation method followed by calcination at 900 °C.22 When the Fe/Mn ratio was increased from 0.1 to 0.3 (FeMn-0.3-450), all diffraction peaks were broadened with the appearance of the impurity phase of α-Fe2O3, similar to the iron-doped spinel prepared by ultrasonic spray pyrolysis at 800 °C.20 The lattice parameters (a) of the samples (0.813−0.819 nm) were not consistent with the published data (0.824−0.828 nm).24 This 3684



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was acidic (pH 2.0) due to release of the protons from the adsorbent into the solution. In order to evaluate the maximum amount of lithium adsorption from the brine, NaHCO3-added brine was used, because NaHCO3 acts as a buffer in the brine (pH value of the brine was 6.5 before and after lithium adsorption). To evaluate the ability of the adsorbents to adsorb lithium ions from the NaHCO3-added brine, batch experiments were performed. A preliminary study of lithium adsorption rate showed that a batch treatment for a day is sufficient to reach adsorption equilibrium. The results of lithium adsorption are presented in Figures 4 and 5. Among the three adsorbents

Figure 2. Li+ extraction with HCl solutions from Fe-doped samples with various Fe/Mn ratios calcined at 450 °C. Li (○), Mn (□), and Fe (Δ).

ratio of 0.1 obtained from calcination at 450 °C. The amount of Mn extracted in HCl solution decreased with increasing Fe/Mn ratio, and the amounts of lithium extraction were 90%, 96%, and 91% for Fe/Mn = 0.1, Fe/Mn = 0.2, and Fe/Mn = 0.3, respectively, while the amounts of dissolved iron showed the opposite trend. Figure 3 shows the lithium extraction from the precursors with Fe/Mn ratio of 0.1 obtained at different calcination Figure 4. Li+ adsorption from the NaHCO3-added brine and Li+ desorption with HCl solutions from Li+ adsorbed samples with various Fe/Mn ratios calcined at 450 °C. (a) Li uptake (●) and Li extracted (○) and (b) Mn extracted (□) and Fe extracted (Δ).

Figure 3. Li+ extraction with HCl solutions from Fe-doped samples (Fe/Mn = 0.1) calcined at different temperatures. Li (○), Mn (□), and Fe (Δ). Figure 5. Li+ adsorption from the NaHCO3-addd brine and Li+ desorption with HCl solutions from Li+ adsorbed samples from Fedoped samples (Fe/Mn = 0.1) calcined at different temperatures. (a) Li uptake (●) and Li extracted (○) and (b) Mn extracted (□) and Fe extracted (Δ).

temperatures. The amounts of lithium extracted were high for precursors calcined at 400−450 °C (90−96%) and tended to decrease with an increase in calcination temperature reaching 63% at 650 °C. It was found that the amount of dissolved manganese was lowest at calcination temperature of 450 °C, while the amounts of dissolved iron were low at 450−650 °C. The compositions of the adsorbents (protonated) based under the condition of electroneutrality10 are given in Table 2. The proton content was evaluated by mass loss of the adsorbents between 100 and 350 °C in TG curves.17 The mean oxidation states of manganese (ZMn) in the adsorbents were nearly equal to 4, independent of the Fe/Mn ratio and calcination temperatures. Figure 1b shows the XRD patterns of the adsorbents with relative intensities of the diffraction peaks similar to the precursors. Lattice constants, a, of the adsorbents slightly decreased after acid treatment preserving the spinel structure of the precursors (Table 2). Also, oxygen/cations ratios in the adsorbents were nearly close to the theoretical value of 1.33 for spinel. Lithium Adsorption from the NaHCO3-Added Brine. The pH value of the raw brine from Salar de Uyuni was 6.7. After addition of NaHCO3 into the brine, the brine pH was 6.5. If the raw brine was used for lithium adsorption, the lithium adsorptive capacity was low (18.1 mg/g), because the final pH

(Figure 4) calcined at 450 °C, the adsorbent with Fe/Mn ratio of 0.1 exhibited the highest lithium uptake of 31 mg/g, comparable to that of H1.33Mn1.67O4.16 The lithium uptake decreased gradually with an increase in Fe/Mn ratio reaching a low value of 15 mg/g for Fe/Mn ratio of 0.3. After the lithium adsorption, the lithium desorption behavior was investigated in a 0.5 mol/dm3 HCl solution. The lithium extraction progressed with nearly 90% by acid treatment. During acid treatment, the amount of manganese extracted was 1.0%, while the amount of iron extracted was the lowest (3.6%) at Fe/Mn ratio of 0.1 (Figure 4). Similar experiments of lithium adsorption in the NaHCO3added brine and lithium desorption with HCl solution were also performed on adsorbents with Fe/Mn ratio of 0.1 obtained from the precursors calcined at different temperatures (Figure 5). The lithium uptake was high for adsorbents obtained from 400−450 °C (∼30 mg/g), and the amounts of lithium desorption were nearly 90%. The amounts of manganese and iron extracted were high for adsorbents calcined at 350 and 400 °C. 3685



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Lithium Adsorption from the NaOH-Added Brine. NaOH solution was added to the brine to evaluate the lithium adsorptive capacity of the adsorbent at different pH values. Since FeMn-0.1-450(H) has the largest lithium uptake from the NaHCO3-added brine, we used it for the following lithium adsorption studies from the NaOH-added brine. The solution pH is an important parameter to obtain quantitative recovery of lithium ions from the brine. The lithium adsorption experiments were performed by a batch method with NaOH-added brines. First, the adsorption kinetic experiment from the NaOH-added brines was conducted to evaluate the adsorption rates of lithium on FeMn-0.1-450(H). It is apparent that the lithium uptake gradually increased with the contact time (Figure 6). The time required to reach the adsorption equilibrium was nearly 24 h. The lithium uptake was 28 mg/ g at the final pH of 7.2.

7.2. Lithium adsorption reaction caused a pH decrease as seen from monitoring the pH difference before and after lithium adsorption (Figure 7). The NaOH (1 mol/dm3)/brine ratio of 0.10 (volume) was selected as the optimal ratio for all subsequent experiments to be discussed later. Effect of Adsorbent Dose on Lithium Adsorption from the NaOH-Added Brine. The amount of the adsorbent added is an important parameter to evaluate the efficiency of lithium recovery from the brine. The effects of the adsorbent dose and final pH on lithium uptake were studied using the NaOHadded brine, and the results are shown in Figure 8. The

Figure 6. Rate of Li+ adsorption from the NaOH-added brine by the adsorbent (Fe-0.1-450(H)). Figure 8. (a) Effect of adsorbent dose on pH variation; (b) Li+ adsorption from the NaOH-added brine by the adsorbent (Fe-0.1450(H)). Final pH (×), Li uptake (●), Li extraction (○).

Effects of NaOH addition into the brine on lithium adsorption are given in Figure 7. When NaOH was not

adsorbent (weight) to brine (volume) ratio was varied from 10 to 50 g/dm3. An increase in the adsorbent dose increased the lithium recovery (%) from the brine, because the number of adsorption sites available for the Li+/H+ exchange reaction increased. However, the lithium uptake decreased with an increase in the adsorbent dose, because of the decrease of final pH to 2.9 at adsorbent dose of 50 g/dm3. Even at final pH 2.9, the lithium uptake was 21 mg/g with lithium recovery of 68% at adsorbent dose of 50 g/dm3. An increment of adsorbent dose beyond 50 g/dm3 would not increase in lithium recovery (%) because of further drop in final pH of the solution. Analysis by the H+/Li+ Ion Exchange Mechanism. The above results can be analyzed on the basis of ion exchange reaction as follows:

Figure 7. Effect of NaOH addition on Li+ adsorption from the raw brine by the adsorbent (Fe-0.1-450(H)). Li uptake (red ●) (■ from ref 16), initial pH (◊), final pH (×).

added into the raw brine, the initial pH 6.5 of the raw brine dropped to pH 2.0 after lithium adsorption because of release of protons from the adsorbent into the solution indicating Li+/ H+ ion exchange reaction.16 The lithium uptake from the raw brine was 18 mg/g at the final pH of 2.0, higher than the 12 mg/g reported for H1.33Mn1.67O4 at the final pH of 2.0.16 The relatively large lithium uptakes for both the adsorbents are due to the presence of small amount of base in the brine. The direct acid titration of the raw brine with HCl solution showed the presence of about 0.03 mol/dm3 base. The addition of NaOH solution into the raw brine caused a gradual increase in lithium uptake accompanied by the increase of final pH of the solution. The maximum lithium uptake was 28 mg/g at the final pH of

H+(s) + Li+(l) → Li+(s) + H+(l) +

+

(i) +

where H (s) and Li (s) are species in the solid phase and Li (l) and H+(l) are those in the solution phase. The equilibrium constant, K, of the above reaction can be defined as28 K = {(H+(l))XLi /XH(Li+(l))}(fLi /fH )

(ii)

where XLi and XH are mole fractions of corresponding species in the solid phase, f Li and f H are activity coefficients in the solid phase, and (H+(l)) and (Li+(l)) are activity of H+ and Li+ in the solution phase, respectively. The selectivity coefficient Kc can be calculated from the experimental results, assuming the 3686



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activity coefficient of Li+ in the solution phase is unity as follows:29 pKc = pH − log(XLi /XH) + log[Li]

with HCl solution, and the adsorbent retained its spinel structure in the protonated form. Using the NaOH-added brine, the regenerated adsorbent showed lithium uptakes of 26−28 mg/g (Figure 10), which were high, but significantly

(iii)

+

where [Li] is concentration of Li in the solution phase. Equilibrium constant K can be evaluated by integrating the pKc vs XLi curve from XLi = 0 to 1. The pKc values calculated from the results in Figures 7 and 8 are plotted as a function of XLi in Figure 9. The pKc values for H1.33Mn1.67O4 and H1.6Mn1.6O4

Figure 10. Regeneration of the adsorbent (FeMn-0.1-450(H)).

lower than the theoretical adsorptive capacity of the adsorbent (54 mg/g). It has been confirmed that all inserted protons in the adsorbent cannot be re-exchanged for lithium ions from the solution and the reverse Li+/H+ exchange proceeds only to ∼60% in the protonated spinel.11 However, these high lithium uptakes of 26−28 mg/g of the regenerated adsorbent were retained even after at least 4 cycles of adsorption/desorption. The amount of manganese extracted (%) in the solution decreased with cycle numbers: 1.1% in the first cycle and 0.70% in the fourth cycle. Although the Fe doping in the adsorbent did not largely change the Mn dissolution during acidtreatment compared to H1.33Mn1.67O4 or H1.6Mn1.6O4 adsorbent, the effective use of Mn and Fe is also a key to the development of the inexpensive adsorbent using manganese mineral containing iron. Comparison of Lithium Adsorption with the Same Adsorbent without Doped. A comparison of lithium adsorption properties between iron-doped adsorbent (Fe/Mn ratio of 0.1) with the same adsorbent without doping (H1.33Mn1.67O4)16 was made under similar conditions of experiments: (i) 2.5 g of adsorbent without doping was treated with 200 cm3 of 0.5 mol/dm3 HCl for Li+ extraction and (ii) 1.0 g of the adsorbent without doping was reacted with 50 cm3 of the raw brine or NaHCO3-treated brine for lithium adsorption. The amounts of Mn extracted (%) during treatments of the precursors with 0.5 mol/dm3 were 3.7% and 4.8% for Fe/Mn ratio of 0.1 and adsorbent without doping, respectively. The total amounts of iron extracted (%) increased with an increase in Fe/Mn ratio of iron-doped adsorbents. The lithium uptake from the NaHCO3-added brine by Fe/Mn ratio of 0.1 and adsorbent without doping was nearly the same (30 mg/g). After treatment of lithium adsorbed samples with 0.5 mol/dm3 HCl solution, the amounts of Mn extracted (%) were 0.9 and 1.1% for Fe/Mn ratio of 0.1 and adsorbent without doping, respectively. Using raw brine at solid−solution ratio of 20 g/dm3 and final pH ∼2, the lithium adsorptive capacity of the adsorbent with Fe/Mn ratio of 0.1 was 18.1 mg/g compared to 13.7 mg/g of adsorbent without doping. This iron-doped adsorbent shows slightly higher selectivity for lithium ions in the raw brine compared to the adsorbent without doping. The lithium adsorption rates by two adsorbents from the brine were nearly the same, requiring 24 h to attain equilibrium.

Figure 9. pKc vs XLi calculated from (red ●) Figure 7 and (●) Figure 8 and (○) H1.33Mn1.67O4 from ref 16 and (Δ) H1.6Mn1.6O4 from ref 16.

were also calculated using the previous results16 in the brine system and are plotted in Figure 9. The pKc values showed similar XLi dependency for all the three adsorbents. In the region XLi < 0.6, the pKc values were nearly constant (about 1) independent of XLi, with the intrinsic pKc values (the pKc value extrapolated to XLi = 0) of about 1. In the region XLi > 0.6, the pKc values increased with XLi; this indicates an increase of energy required for H+/Li+ exchange with XLi, probably due to the steric interactions among the adsorbed Li+ in the solid phase. It is interesting that the pKc vs XLi curves in the present brine system resemble those obtained by pH titration in the (0.1 M LiCl + LiOH) system;28 in both systems, the pKc values were constant in the low XLi region and increased with XLi in the high XLi region. This indicates that the Li+ adsorption in the brine system progressed by the ion-sieve mechanism the same as that in the 0.1 M LiCl system although the brine contains enormous amounts of NaCl, KCl, MgCl2, and sulfate salt. Adsorption of Other Metal Ions. The adsorption of Li+, Na+, K+, Mg2+, and Ca2+ in the FeMn-0.1-450(H) from the NaOH-added brine was determined after dissolving the solid in HCl and H2O2 solution. The Li+ uptake was high (28 mg/g, 4.0 mmol/g), while the uptakes of other metal ions were low: Na = 0.74 mg/g (0.03 mmol/g), K = 0.65 mg/g (0.02 mmol/g), Mg = 1.66 mg/g (0.07 mmol/g), and Ca = 0.85 mg/g (0.02 mmol/ g). The high lithium adsorptive capacity of the adsorbent can be explained by the lithium ion-sieve property of the adsorption sites formed in the crystal lattice of the spinel.30 The adsorption sites of the spinel are so narrow that the cations such Na+ (0.102 nm), K+ (0.138 nm), and Ca2+ (0.100 nm) having larger ionic radii than Li+ (0.074 nm) are excluded from the sites due to steric effect.30 With regard to ionic radius of Mg2+ (0.072 nm) being close to that of Li+ (0.069 nm), a high energy may be required for dehydration of Mg2+ ions to enter the adsorption sites because the free energy of hydration for Mg2+ (ΔGh0 = −1980 kJ/mol) is 4 times greater than Li+ (ΔGh0 = −475 kJ/mol).31 Regeneration. The adsorbent (FeMn-0.1-450(H)) can be easily regenerated by treating the lithium-adsorbed product 3687



Article

Manganese Oxides Determined by X-ray Absorption Spectrometry. Chem. Mater. 1996, 8, 2799. (12) Chitrakar, R.; Kanoh, H.; Miyai, Y.; Ooi, K. Recovery of Lithium from Seawater Using Manganese Oxide Adsorbent (H1.6Mn1.6O4) Derived from Li1.6Mn1.6O4. Ind. Eng. Chem. Res. 2001, 40, 2054. (13) Nishihama, S.; Onishi, K.; Yoshizuka, K. Selective Recovery Process of Lithium from Seawater Using Integrated Ion Exchange Methods. Solvent Extr. Ion Exch. 2011, 29, 421. (14) Xiao, G.; Tong, K.; Zhou, L.; Xiao, J.; Sun, S.; Li, P.; Yu, J. Adsorption and Desorption Behavior of Lithium Ion in Spherical PVC−MnO2 Ion Sieve. Ind. Eng. Chem. Res. 2012, 51, 10921. (15) Wajima, T.; Munakata, K.; Uda, T. Adsorption Behavior of Lithium from Seawater Using Manganese Oxide Adsorbent. Plasma Fusion Res. 2012, 7, 2405021. (16) Chitrakar, R.; Makita, Y.; Ooi, K.; Sonoda, A. Selective Uptake of Lithium Ion from Brine by H1.33Mn1.67O4 and H1.6Mn1.6O4. Chem. Lett. 2012, 41, 1647. (17) Liu, Y. F.; Feng, Q.; Ooi, K. Li+ Extraction/Insertion Reactions with LiAlMnO4 and LiFeMnO4 Spinels in the Aqueous Phase. J. Colloid Interface Sci. 1994, 163, 130. (18) Ohzuka, T.; Ariyoshi, K.; Takeda, S.; Sakai, Y. Synthesis and Characterization of 5 V Insertion Material of Li[FeyMn2‑y]O4 for Lithium-Ion Batteries. Electrochim. Acta 2001, 46, 2327. (19) Mateyshina, Y. G.; Lafont, U.; Uvarov, N. F.; Kelder, E. M. Physical and Electrochemical Properties of Iron-Doped Lithium− Manganese Spinels Prepared by Different Methods. Solid State Ionics 2008, 179, 192. (20) Ebin, B.; Gurmen, S.; Arslan, C.; Lindbergh, G. Electrochemical Properties of Nanocrystalline LiFexMn2−xO4 (x = 0.2−1.0) Cathode Particles Prepared by Ultrasonic Spray Pyrolysis Method. Electrochim. Acta 2012, 76, 368. (21) Taniguchi, I.; Bakenov, Z. Spray Pyrolysis Synthesis of Nanostructured LiFexMn2−xO4 Cathode Materials for Lithium-Ion Batteries. Powder Technol. 2005, 159, 55. (22) Hernan, L.; Morales, J.; Sanchez, L.; Castellon, E. R.; Aranda, M. A. G. Synthesis, Characterization and Comparative Study of the Electrochemical Properties of Doped Lithium Manganese Spinels as Cathodes for High Voltage Lithium Batteries. J. Mater. Chem. 2002, 12, 734. (23) Chukhrov, F. V.; Gorshkov, A. I.; Rudnitskaya, E. S.; Beresovskaya, V. V.; Sivtsov, A. V. Manganese Minerals in Clays: A Review. Clays Clay Miner. 1980, 28, 346. (24) Gracia, M.; Marco, J. F.; Gancedo, J. R.; Ortiz, J.; Pastene, R.; Gautier, J. L. Characterization of the Lithium−Manganese Ferrite LiFeMnO4 Prepared by Two Different Methods. J. Phys. Chem. C 2010, 114, 12792. (25) Mateyshina, Y. G.; Uvarov, N. F.; Ulihin, A. S.; Pavlyukhin, Y. T. Electrochemical Modification of Spinel Oxide Materials Using Lithium Solid State Electrolyte. Solid State Ionics 2006, 177, 2769. (26) Cormack, A. N.; Lewis, G. V.; Parker, S. C.; Catlow, C. R. A. On the Cation Distribution of Spinels. J. Phys. Chem. Solids 1988, 49, 53. (27) Deng, B.; Nakamura, H.; Zhang, Q.; Yoshio, M.; Xia, Y. Greatly I m p r o v e d E l e v a t e d - T e m p e r a t u re C y c l in g B e h a v i o r o f Li1−xMgyMn2−x−yO4+δ Spinels with Controlled Oxygen Stoichiometry. Electrochim. Acta 2004, 49, 1823. (28) Chitrakar, R.; Kanoh, H.; Miyai, Y.; Ooi, K. A New Type of Manganese Oxide (MnO2·0.5H2O) Derived from Li1.6Mn1.6O4 and Its Lithium Ion-Sieve Properties. Chem. Mater. 2000, 12, 3151. (29) Ooi, K.; Miyai, Y.; Katoh, S.; Maeda, H.; Abe, M. The pH Titration Study of Lithium Ion Adsorption on λ-MnO2. Bull. Chem. Soc. Jpn. 1988, 61, 407. (30) Umeno, A.; Miyai, Y.; Takagi, N.; Chitrakar, R.; Sakane, K.; Ooi, K. Preparation and Adsorptive Properties of Membrane-Type Adsorbents for Lithium Recovery from Seawater. Ind. Eng. Chem. Res. 2002, 41, 4281. (31) Marcus, Y. Thermodynamics of Solvation of Ions Part 5.-Gibbs Free Energy of Hydration at 298.15 K. J. Chem. Soc. Faraday Trans. 1991, 87, 2995.

4. CONCLUSIONS Among the adsorbents studied, the adsorbent with Fe/Mn ratio of 0.1 obtained from calcination of the precursor at 450 °C showed the highest lithium extractability with HCl solution. The adsorbent showed lithium uptake of 18.1 mg/g from the raw brine at final pH 2.0 (initial pH 6.7), and the uptake increased to 28 mg/g at final pH 7.2 after addition of 1 mol/ dm3 NaOH solution into the raw brine (initial pH 8.2). The adsorbent can be easily regenerated with HCl solution with 90% lithium extraction. The adsorbent exhibited remarkably high lithium adsorptive capacity and selectivity for lithium ions in the brine because of narrow adsorption sites which excludes the sodium, potassium, magnesium, and calcium with ionic radii larger than the ionic radii of lithium ions. The adsorbent is inexpensive, stable in acid with low dissolved manganese and iron, highly selective for lithium ions in the raw brine, easily regenerated, and reusable several times as lithium adsorbent.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +81-87-869-3572. Fax: +81-87-869-3553. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Japan Oil, Gas and Metals National Corporation (JOGMEC). REFERENCES

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